1. Field of the Invention
The invention relates to pumping molten metal and more particularly to molten metal pump apparatus and methods for assembling and disassembling such apparatus.
2. Brief Description of Prior Art
A molten metal pump apparatus generally includes a motor mounted above a molten metal bath. The motor drives a rotatable impeller pump having one or more impellers submerged in the bath. In operation, the rotating impellers draw molten material from the bath and pump it through a conduit routed to a subsequent station for further processing.
The molten metal pump typically includes a base having inlet and outlet passages for intake and discharge of the molten metal being pumped. The pump base together with the impeller are submerged in the molten metal, supported on the bottom of the vessel containing the molten metal. The pump base is typically connected by refractory cement and/or mechanical arrangements to a plurality of vertically extending support posts which are also connected to a drive arrangement positioned above the level molten metal. In typical installations, these vertically extending posts may be several feet long, e.g. one to four feet in length or longer, in order to provide adequate clearance between the molten metal level.
The portions of the pump assembly submerged in the molten metal are directly contacted and exposed to the harsh conditions thereof, and are formed of refractory material such as graphite, silicone carbide, alumina, zirconia or hexalloy. The posts extend through a level of the molten metal and are connected to a motor mounting plate of the drive arrangement positioned above the level molten metal.
In prior art arrangements, downwardly opening post sockets are fixed to the motor mounting plate and receive the upper ends of the posts. One or more post sockets may be fixed to a post support plate, as by welding, and the support plate is secured to the motor mounting plate. In prior art arrangements, the posts may also be secured within the post's sockets by means of a refractory cement, bolts or other clamping devices.
Despite the positive properties for this described application, graphite and ceramics still corrode and deteriorate over time, and molten metal pumps must be more frequently maintained and replaced than other types of pumps. The replacement or servicing of a pump having operating components submersed in molten metal is a time consuming exercise. First, the pump must be removed from the molten metal which generally causes down time. Then the pump along with the molten metal contained thereon must be allowed to sufficiently cool to allow it to be disassembled. Once the deteriorated components are sufficiently cooled, the molten metal buildup on the various pump surfaces must be sufficiently removed to allow disassembly and/or re-use of the pump components. Then the pump must be reassembled with the combination of old components or parts, along with the replacement parts.
As previously described, there are certain components of the pump which are typically cemented together in order to achieve a balanced and sufficiently rigid pump structure to allow continuous operation of the pump. However, when the pump must be disassembled, the cemented joints can be very difficult to disassemble.
In the case of the vertical posts between the pump base and the motor mount structure, the posts have traditionally been cemented into bored holes within the base. In the case of the base for example, when the pump is disassembled, the cemented portion of the posts must normally then be chipped, dug or drilled out in order to allow a new post to be placed in the same bore. This makes the disassembly much more difficult. A most significant disadvantage to prior art arrangements is therefore the need to cleanly remove the post when it is necessary to replace the post.
Further, during assembly of the pump, it is important that the pump components be accurately aligned in order for the pump system to work efficiently once it is back in the molten metal. The combination of the components are very heavy, and once the posts for example are cemented in place as described above, it is then very difficult if not impossible to align if necessary.
It is an object of the present invention to provide a pump which does not require as many or any cemented joints as the prior art pumps. It is also an object of the present invention to provide a pump and assembly system which tends to self-align the pump during the assembly process due to its design and configuration, possibly reducing or eliminating the need for alignment apparatuses.
As will be seen from the subsequent description, the preferred embodiments of the present invention overcome shortcomings of the prior art.